A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simplified network architecture. LTE systems also provide seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of base stations, e.g., evolved Node-Bs (eNBs) communicating with a plurality of mobile stations referred as user equipments (UEs).
The LTE system, however, is optimized for data transfer. It is designed as a packet switch all-IP system without any circuit switched domain currently used for regular voice services. Even with the rapid growth of the data communication over the network, the wireless voice business is still the main source of revenue for operators. For operators evolving to LTE, providing voice on one network and data on another does not make financial sense. Voice will become an integral part of LTE. Voice over LTE provides such services for the operators to offer telecom grade voice, video calling and other new richer communication services on LTE Smartphones.
One of the challenges to provide telecom grade voice and video call over LTE is to shorten the call set-up time. In voice over LTE, when a voice or a video call is initiated, the UE needs to negotiate codec and reserve bearer for the communication. This is required for both mobile originated (MO) and mobile-terminated (MT) calls. The codec negotiation may take several rounds. For example, Session Description Protocol (SDP) is one common way for codec negotiation in voice over LTE. The caller will first send its codec information to the callee through a first SDP offer message. The callee, upon receiving the first SDP offer message, may not be able to find a match and would reject the first SDP offer. The caller will then need to proceed with a second SDP offer. The SDP negotiation has to be complete before the call can be successfully set up. Improvements are needed to shorten the SDP negotiation time.
Second, initial resource allocation also delays call set-up for voice LTE. In the current system design, resource allocation is initiated by the network. UE is refrained from requesting additional evolved packet system (EPS) bearer context for media unless the UE detects that the network does not initiate resource allocation for the media. The UE detects the failure of the network allocation relying on a timer. The SDP negotiation and initial resource allocation delay the call set-up for voice over LTE. Improvements are needed to shorten the call set up time.